Are you saying all the areas of the map in GTAV are open up at the beginning of the game?

I'm really on the fence with this one, I start school up next Wednesday and I'm not really sure I want the distraction.

Also a question? How's the gunplay in this game? It's one of the things that really killed part 4 for me. I was hoping it'd be closer to Red Dead Redemption, because that was the first (and so far only) open sandbox Rockstar game that I have beaten.